Lipsticks are primarily composed of hydrocarbon waxes, esters of fatty acids or alcohols and oils. Water and other polar solvents, such as glycerine and propylene glycol, which can provide moisturization benefits are not soluble in this lipophilic matrix. As a result, various emulsifiers have been added to lipsticks in an attempt to emulsify the moisturizers/polar solvents. There has been partial success in this area by utilizing the emulsifiers and moisturizers/polar solvents at low concentrations. However, the moisturizers/polar solvents may separate from the lipstick causing it to look wet and messy. This is unacceptable to the consumer.
Thus a need exists to provide a lipstick which binds thermodynamically the moisturizers/polar solvents (discontinuous phase) and deliver them in a predominately nonpolar lipophilic matrix (continuous phase). Further, there is a need to provide a means of thermodynamically binding the moisturizers/polar solvents in such a way which will allow incorporation of high levels of the moisturizing agents while exhibiting overall excellent stability and providing good feel properties.
It has been discovered that association structures consisting essentially of a surfactant or mixture of surfactants having a Krafft point at or below about ambient temperature (about 20.degree. C.) and a moisturizer/polar solvent can thermodynamically bind the moisturizer/polar solvent and homogeneously absorb in the lipophilic matrix while providing good feel and a means of delivering the moisturizing agents to the lips. Thus, the association structures of this invention can be used to deliver the moisturizers/polar solvents without syneresis, the separation of the hydrophilic materials. It has been discovered that upon application to the lips the preferred association structures of the present invention form a film on the lips which can act as a reservoir for the moisturizer/polar solvent.
It is particularly desirable that the lipsticks comprising said association structures be made from ingredients that are presently used and approved for use in edible product applications and for applying to the skin. It is an object of this invention to provide a delivery system for moisturizers/polar solvents through the nonpolar matrix of the lipstick while providing good feel. It is another object of this invention to provide a lipstick composition which can be easily molded yet contain high levels of moisturizers.
Sweating, the excretion of oil on the surface of a lipstick, is a common problem. Lipsticks are a complex mixture of solid, semi-solid and liquid lipids. Wax networks suspend the oils present in the lipstick. Sweating occurs due to the inferior oil-binding capacity of the wax network and/or to a high oil content causing supersaturation. The phenomenon can occur in any climate or temperature; although, it is more apt to occur in sub-tropical and tropical climates.
In most cases, castor oil has been identified as the excreted oil. A major ingredient of most lipstick formulations, castor oil can generally comprise up to forty percent of lipsticks. The high percentage of castor oil is primarily due to its unique properties as a wetting agent for pigments. Monodispersions of pigments are commonly made in slurries comprising from about 30% to about 40% pigments and from about 60% to about 70% castor oil.
It is an object of this invention to provide a preferred lipstick composition of the present invention which is substantially free of castor oil. It is an object that the lipstick be castor oil sweat resistant or castor oil sweat free. An added benefit to removing the castor oil is the removal of the castor oil odor.
It has been discovered that the association structures, preferably lamellar liquid crystals (neat phase), can be used to deliver moisturizing agents in lipsticks which are substantially free of castor oil. It has been found that removal of the castor oil, typically present in the range of from about 30% to about 50% of the lipstick compositions, allows for optimization of emollients; thus, providing for a more consumer acceptable feel, such as less tackiness, and moisturizing benefits by utilizing more lubricious emollients.
All percentages and ratios stated herein are by weight unless otherwise indicated.